Disk playback apparatus with centering device for different disk sizes

ABSTRACT

A disk playback apparatus with a centering mechanism for positioning a small or a large disk which comprises a support frame, a clamper arm swingably mounted on a rear portion of the support frame, and a centering mechanism for guiding large and a small diameter disks from a front side of the playback apparatus to a position between the support frame and the clamper arm when the disk is inserted into the playback apparatus. The centering mechanism has a pair of centering arms for contacting with a circumferential edge of the disk for positioning the disk in place, a centering lever provided in the clamper arm and connected to the pair of centering arms for simultaneously opening/closing the pair of centering arms, and lock arms each rotatably mounted on the associated centering arm for locking the centering arm independently, the lock arms allowing the pair of centering arms to be swingable when both the lock arms are released. This playback apparatus can center both the small and large size disks at a clamp position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disk playback apparatus provided witha centering mechanism for accurately and consistently positioning adisk, which has been inserted therein, at a clamp location on aturntable.

2. Description of the Related Art

Recently, there has been provided a compact disk referred to as a diskhereinafter in which analog sound are converted into digital signals andthen pits corresponding to the digital signals are formed in a recordinglayer thereof. With such a disk, analog sound may be opticallyreproduced by a laser beam emitted from an optical head of the CDplayer. Also, in comparison with a conventional LP record, the disk isextremely superior in sound quality and operational properties.Accordingly, the disk has been widely used together with the CD player.In particular, CD players have been developed for automotive use. When adisk having a diameter of 12 cm for playback of music is inserted into adisk insertion opening, the disk is loaded toward a predeterminedposition (the substantially central position of the CD player) by aloading mechanism. When the disk is brought into contact with a stopportion provided within the CD player, the loading operation is stoppedto position the disk in place. In this position, the disk is fixed ontoa turntable by means of a clamper arm. The disk on the turntable isrotated by a spindle motor, and the music recorded in the disk isreproduced by a readout head.

On the other hand, a disk having a much smaller diameter of 8 cm hasbeen recently developed. However, if it is desired to insert such a diskinto the insertion opening of the conventional CD player, the operatormust pay special attention to the operation because the width of theinsertion opening is too large.

Also, in a conventional CD player, since the stop portion for stoppingthe inserted disk at the clamp position is provided for positioning thelarge diameter disk, when the smaller disk is transferred into contactwith the stop portion, the smaller disk would be advanced beyond theclamp position.

Accordingly, there has been proposed a centering system for guiding thesmall diameter disk to the center of the disk insertion opening. In thiscase, a disk guide plate has been provided below the clamper arm forguiding the small disk to the clamp position.

However, if such a centering mechanism is provided at the disk insertionopening, the overall mechanism of the player becomes complicated. Also,in a conventional disk player, after the centering operation of the diskhas been performed at the disk insertion opening, the disk istransferred to the clamp position. As a result, there is a possibilitythat the disk would be likely to be displaced or offset during clampingso that it would be difficult to accurately clamp the disk at thedesired position. Furthermore, when a larger disk is inserted into theplayer, the disk must be brought into contact with the centeringmechanism, and the operator must push the disk to open the centeringmechanism. This can be cumbersome to the operator.

SUMMARY OF THE INVENTION

In view of the foregoing difficulties, an object of the presentinvention is to provide a disk playback apparatus having a centeringmechanism that may more accurately center an inserted small or largediameter disk at a clamp position.

According to the present invention, there is provided a disk playbackapparatus having: a support frame, a clamper arm swingably mounted on arear portion of the support frame, and a centering mechanism for guidinga large and small diameter disks from a front side of the playbackapparatus to a position between the support frame and the clamper armwhen the disk is inserted into the playback apparatus. The centeringmechanism includes: a pair of centering arms swingably provided on theclamper arm on a side of the support frame and having contact portionsfor contacting with a circumferential edge of the disk for positioningthe disk in place. A centering lever is provided on the clamper arm andconnected to the centering arms for simultaneously opening/closing thepair of centering arms. Lock arms are rotatably mounted on theassociated centering arm for locking the centering arm independently,the lock arms allow the pair of centering arms to be swingable when onlywhen both the lock arms are released.

When a small disk is inserted into the playback apparatus, if the diskis displaced from the center, one of the lock arms is angularly moved torelease the locking condition. However, in this case, the other lock armis not released but is kept under the locking condition. Accordingly,the other centering arm is not swung. The disk centered in contact withthe latter centering arm is guided to a regular clamp position.

On the other hand, if large diameter disk is inserted into the playbackapparatus, both lock arms are angularly moved to release the lockingcondition by circumferential edge of the disk. In this case, both thelock arms are released to release the lock mechanism. While thecircumferential edge of the disk is being brought into contact with thecontact portions of the centering arms, the centering arms are equallyopened to thereby perform the centering and guide operationsimultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a perspective view showing a disk playback apparatus accordingto the invention;

FIG. 2 is a perspective view showing a support frame shown in FIG. 1;

FIG. 3 is a top plan view showing a clamper arm when a small disk isinserted into the apparatus;

FIG. 4 is a top plan view showing the clamper arm when a large disk isinserted into the apparatus;

FIG. 5 is a perspective view showing a disk guide;

FIG. 6 is a perspective view showing a lock arm;

FIG. 7 is an enlarged view showing a lock release mechanism of the lockarm;

FIG. 8 is a side view showing an operation of the escape arm and atranslation arm;

FIG. 9 is a side view showing the operation of the escape arm and thetranslation arm;

FIG. 10 is a top plan view showing the operation of a detecting pin;

FIG. 11 is a cross-sectional view showing the guide member; and

FIG. 11 is a perspective view showing the guide member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of the invention will now be described with reference tothe accompanying drawings.

FIGS. 1 though 12 show a CD player according to the embodiment of theinvention. In FIG. 1, a disk insertion opening 2 is formed in a frontface of a casing 1 of the CD player to which the present invention isapplied. A frame 3 is received in the casing 1. This frame 3 has asubstantially planar ceiling plate 3a and side plates 3b, 3b each ofwhich is bent downwardly from the ceiling plate 3a. Inside the frame 3,a support frame 4 is arranged as shown in FIG. 2. A playback device (notshown) for reproducing a piece of music recorded in a disk is disposedsubstantially at the center of the support frame 4. The support frame 4is floatingly supported on the frame 3 through dampers 5. A loadingmechanism 6 for transferring a disk 106 or 101 having a large or smalldiameter of 12 cm or 8 cm respectively to a predetermined position(i.e., center of the support frame 4) and a loading arm swing mechanism7 for swinging a loading arm 8 are provided on a front side portion ofthe frame 3. The loading mechanism 6 has a drive roller 9 mounted on thesupport frame 4.

As shown in FIGS. 11 and 12, above the drive roller 9, there is provideda disk guide means such as a guide member 51 for guiding the disk 101 or106. The guide member 51 has a guide recess S. The opposite end portionsS₀ and S₀ of the guide recess S are brought into contact with acircumferential portion of the large disk 101 and serve to transfer thelatter. Surfaces S₁ and S₁ inside the end portions S₀ and S₀ are broughtinto contact with a circumferential portion of the small disk 106 andserve to transfer the latter. Also, the quide member 51 is made ofsynthetic resin or the like. As best shown in FIG. 12, a horizontalguide surface 52 extending in the same direction of the openingdirection of the disk insertion opening 2 in a curved manner and keptsubstantially in parallel to the transfer direction of the disk isformed in the lower surface of the guide member 51 (the horizontal guidesurface extends horizontally in section as shown in FIG. 11). A gentlyslanted surface 53 is extended adjacent the horizontal guide surface 52in the rear portion thereof and a short slanted groove 54 in the frontportion thereof.

The slanted surface 53 serves to introduce a front end portion of thedisk 101 or 106, inserted into the disk insertion opening 2, between theguide member 51 and the drive roller 9. The horizontal guide surface 52serves to guide the disk 101 or 106, positioned between the guide member51 and the drive roller 9, in the disk insertion direction in parallel.The slanted groove 54 serves to guide the disk 106 having a diameter of8 cm toward a disk guide plate which will be described later. A width W₀of the slanted groove 54 is set so that the small disk 106 is insertedinto the slanted groove 54 immediately before the small disk 106 reachesthe clamp position but the large diameter disk 101 is not inserted intothe slanted groove 54.

The axis of the drive roller 9 is located somewhat in front of a pointimmediately below a transit point P between the horizontal guide surface52 and the slanted groove 54 with respect to the disk transfer directionas shown in FIG. 11. The disk 106 inserted into the disk insertionopening 2 is guided in parallel to the disk insertion direction alongthe horizontal guide surface 52, and thereafter is guided into theslanted groove 54. As a result, the forward end of the disk 106 israised and the disk 106 is guided toward the disk guide plate to bedescribed later. The large diameter disk 101 is not guided into theslanted guide groove 54 even if the large disk 101 is guided by theguide recess 52 but the large diameter disk 101 is transferredhorizontally along the horizontal guide surface 52.

On the other hand, the loading mechanism 6, the loading arm swingmechanism 7 and a lock mechanism 45 to be described later are describedin Japanese Utility Model application No. 62-136632 assigned to thepresent assignee. Also, the loading motor 10 is provided in the frontside of the frame 3. When the drive roller 9 is rotated by the drive ofthe loading motor 10, the disk 106 inserted into the disk insertionopening 2 is transferred to a predetermined position.

As shown in FIG. 1, a photo sensor 47 is provided in the vicinity of thedisk insertion opening 2 substantially at the center of the ceilingplate 3a of the frame 3. It is possible to detect, by the photo sensor47, whether or not the disk 106 is inserted into the disk insertionopening 2. When the photo sensor 47 detects the insertion of the disk106, a signal from the photo sensor 47 is outputted to a control circuit(not shown), so that the loading motor 10 is driven by the controlcircuit. When the loading motor 10 is driven, the disk 106 istransferred by the cooperation between the drive roller 9 and the guidemember 51.

A turntable 29 on which the disk 106 is to be loaded is provided in themiddle of the support frame 4 as shown in FIG. 2. The turntable 29 isdrivingly rotated by a spindle motor 30 provided on a lower side of thesupport frame 4. A small disk-like clamper 31 is located above theturntable 29. The clamper 31 is provided at a triangular projecting endof a clamper arm 32 which is swingably mounted on a rear portion of thesupport frame 4. A tension spring (not shown) is laid between theclamper arm 32 and the support frame 4 so that the clamper arm 32 isurged toward the turntable 29.

Also, as shown in FIGS. 3 and 4, the disk guide plate 34 for guiding thesmaller diameter disk 106 of 8 cm to the clamp position when the disk106 is transferred on the turntable 29 is provided on the inner surfaceof the clamp arm 32. Also, as shown in FIG. 5, a disk guide recess 35 isformed in the lower side and the central portion of the disk guide plate34. This disk guide recess 35 is opened toward the disk insertionopening 2. An opening width of the disk guide recess 35 on the side ofthe disk insertion opening 2 is set so as to receive the small disk 106.Also, an arcuate circumferential wall 35a is provided in the guiderecess 35. Also, as shown in FIG. 3, a centering lever 61 which is asubstantially T-shaped member is provided on the upper surface of theclamper arm 32. Two elongated holes 61b, 61b extending in the slidingdirection of the centering lever 61 are formed in the central portion ofthe central lever 61. The elongated holes 61b, 61b engage with pins 32d,32d formed in the clamper arm 32, respectively. Two holes 61a, 61a areformed in the opposite sides of the centering lever 61.

Subsequently, the structure of the centering mechanism which issymmetrical with respect to the center axis thereof in FIG. 3 will beexplained as to the centering mechanism on the left side in FIG. 3. Acentering arm 62 is provided in a lower surface of the clamper arm 32. Apin 62a of the centering arm 62 swingable about a pivot arm 62c isloosely engaged with the hole 61a. The pin 62a is formed at one endportion of the centering arm 62. Also, at the other end of the centeringarm 62 (i.e., the front side end portion thereof), there is downwardlyprojected a centering pin 62b which is in contact with thecircumferential portion of the disk and is used as a contact portionwith the disk. In this case, a distance between the right and leftcentering pins 62b is set so that, when the small disk of 8 cm diameteris centered, the centering pins 62b do not come into contact with thecircumferential portion of the disk of 8 cm. Furthermore, the lock arm63 which is substantially in the shape of a triangle is rotatablyprovided on the centering arm 62 about the centering pin 62b (FIG. 6).The lock arm 63 has an opening 63c in the central portion thereof asbest shown in FIG. 6. An engagement piece 62d mounted on the tip end ofthe centering arm 62 is engaged with the opening portion 63c. Thisstructure is used as a stop mechanism against the rotation of the lockarm 63. Furthermore, the centering pin 62b passes through a one-cornerportion. Also, the lock arm 63 has a lock pin 63a, for locking the swingmotion of the centering arm 62, projecting upwardly at another cornerportion of the lock arm 63 and a lock release pin 63b projectingdownwardly of the other corner portion for releasing the lock condition.The lock arm 63 is always spring-biased inwardly by a lock arm biasingspring 64 interposed between the centering arm 62 and the lock arm 63.Namely, the lock arm 63 is biased in the direction in which the lock pin63a is engaged with a lock recess portion 32b of an opening portion 32aopened in the clamper arm 32 shown in FIG. 7. With such a structure, thelock arm 63 is normally kept under the condition that the lock pin 63ais engaged with lock recess portion 32b. As described above, the likestructures are provided in the right and left sides of the player toform the centering mechanism substantially in a symmetrical manner.

Also, an escape arm 66 is provided swingably about a swing center 66a inthe clamper arm 32. One end portion of the escape arm 66 is engaged witha projection 61P of the right side portion of the centering lever 61.The escape arm 66 is always biased clockwise in FIG. 3 by an escapespring 67 interposed between the escape arm 66 and the clamper arm 32.With such an arrangement, the centering lever 61 is biased rearwardly,so that the pair of right and left centering arms 62 are biasedinwardly. The other end portion (i.e., outward end) of the escape arm 66is projected outside of the clamper arm 32 and is engaged with aconverting arm 68.

FIGS. 8 and 9 are enlarged side views showing a structure of theconverting arm 68. The converting arm 68 is so constructed that it isretained at a position different from that of the outer portion of theescape arm 66. The converting arm 68 is swingably provided to thesupport frame 4 through a pivot pin 68a. Also, an upper portion of theconverting arm 68 has a first projection 68b and a second projection68c. Furthermore, an engagement pin 68d is provided on a surface of theconverting arm 68 opposite to the swing pin 68a and is engaged with aguide groove 32c provided in a suitable position of the clamper arm 32to thereby limit the swing range of the clamper arm 32.

Also, in the left part of FIG. 3, a disk detecting arm 69 for the disk106 of 8 cm is provided coaxially with the pivot arm 62c of thecentering arm 62 in the lower portion of the clamper arm 32. A diskdetecting portion 69a is provided at a suitable position of the diskdetecting arm 69 for the disk of 8 cm. The disk detecting portion 69a isbiased by a disk detecting arm spring 70 so that it is always projectedfrom the circumferential wall 35a of the guide recess 35 to the diskreceiving portion.

As shown in FIG. 10, a detection pin 41 is mounted on one end of a firstlink 42 which forms a part of a linkage mechanism pivotally formed on arear side of the frame 3. The other end of the first link 42 pivotallymounted around a pin 142 is coupled to a second link 43 mountedslidingly in the disk insertion direction. When the detecting pin 41 isdepressed by the disk detecting arm 69 for the small diameter disk 106and is depressed directly by the disk for the large diameter disk 101,the second link 43 is slidingly moved to thereby operate the loading armswing mechanism 7 to lower the loading arm 8 with a pin 150 engagingwith a projecting arm 32c (FIG. 2) whereby the clamper 32 is lowered.

On the other hand, as shown in FIGS. 1 and 2, a lock pin 44 is implantedin the side end of the support frame 4 and extends toward the frame 3.The lock mechanism 45 is provided in the frame 3 from which the lock pin44 projects. The lock pin 44 is locked by the lock mechanism 45 untilthe inserted disk is transferred to the predetermined position. Thesupport frame 4 is fixedly supported by the frame 3 when the lock pin 44is locked. When the loading arm 8 is moved downwardly by the operationof the loading arm swing mechanism 7, the lock mechanism 45 is used torelease the lock condition of the lock pin 44, and the support frame 4is floatingly supported by the frame 3 through the dampers 5 when thelock pin 44 is released.

A movable cover 46 is openable/closable and is mounted on the frame 3 inthe vicinity of the disk insertion opening 2. During the use of the CDplayer, the movable cover 46 is moved to the disk insertion opening 2 tothereby prevent another disk from being erroneously inserted into thedisk insertion opening 2.

The operation of the above-described embodiment will now be described.

When the small diameter disk 106 is inserted into the disk insertionopening 2, the sensor 47 provided at the front portion of the ceilingplate 3a detects the insertion thereof to thereby drive the loadingmotor 10. The drive roller 9 is rotated by the loading motor 10. Thesmall disk 106 is clamped between the guide member 51 and the driveroller 9 while being roughly centered, and the disk 106 is transferredtoward the turntable 29 by the roller 9.

When the small diameter disk 106 is inserted while being somewhatdisplaced to the left as shown in FIG. 3, the circumference of the disk106 is brought into contact with the lock release pin 63b provided inthe left centering arm 62. As a result, the lock arm 63 is rotated inthe direction in which the locking state is released (in the clockwisedirection in FIG. 7). However, under this condition, the circumferenceof the disk 106 causes one of the lock arms 63 to rotate but the otherlock arm 63 is kept under the locking state so that the locking state ofthe centering arms 62 is not released. Thus, the disk 106 is enteredpositively into the disk guide recess 35 of the disk guide plate 34provided on the lower surface of the clamper arm 32 while beingdisplaced to the right in contact with the centering pin 62b and beingdirected upward by the guide member 51 and the guide roller 9 as shownin FIG. 11. As a result, the centering operation is performed.

When the disk 106 is inserted into the disk guide recess 35, it isbrought into contact with the arcuate circumferential wall 35a andguided to the center of the disk guide recess 35 along thecircumferential wall 35a. When the disk 106 is guided to the center ofthe disk guide recess 35, as shown in FIG. 10, the disk detectingportion 69a of the disk detecting arm 69 for the disk of 8 cm, projectedfrom the circumferential wall 35a is pushed. When the disk 101 isinserted in the middle of the disk insertion opening 2, the disk 101causes the opposite lock arms 63 to be released substantiallysimultaneously and to be opened toward the outside to allow theinsertion of the large diameter disk 101.

The thus inserted large diameter disk 101 is brought into direct contactwith the detecting pin 41 as shown in FIG. 10 because the large diameterdisk 101 is moved horizontally without contacting the disk guide recess35.

Also, when the large diameter disk 101 is inserted, the oppositecentering arms 62 are swung, the centering lever 61 is slidingly movedon the clamper arm 32. As a result, an escape arm 66 is swung in thecounterclockwise direction in FIG. 4 against an escape arm spring 67about a pivot center 66a. Under this condition, the clamper arm 32 isswung relative to the support frame 4 to thereby clamp the largediameter disk 101. In this case, an end portion of the escape arm 66 isbiased to be depressed against the second projection 68c by the escapearm spring 67 as indicated by the two-dotted and dash line in FIG. 9.With such a structure, the centering arms 62 which are normally urgedinwardly by the escape arm spring 67 may be fixedly supported in place.Thus, during the playback of the large diameter disk 101, the centeringpins 62b are prevented from coming into contact with the disk 101. Also,in the case of the small disk 106, the escape arm 66 is urged to bedepressed against the first projection 68b of the converting arm 68 bythe escape arm spring 67. With such an arrangement, it is possible toprevent the centering pins 62b from coming into contact with the smalldisk 106.

Also, when the detecting pin 41 is depressed, as shown in FIG. 10, thefirst link 42 is pivoted about the pin 142 to thereby swing the secondlink 43 so that the pin 150 fixed to the loading arm 8 is released tothereby actuate the loading arm swing mechanism 7. Accordingly, as shownin FIG. 2, the side projecting piece 32c of the clamper arm 32 which isin contact with the loading arm 8 is lowered together with the loadingarm 8 so that the clamper arm 32 is lowered by the spring force. As aresult, the disk 101 or 106 loaded on the turntable 29 is depressed andfixed by the clamper 31. The disk 101 or 106 is fixed by the clamper 31,and the lock mechanism 45 releases the locking condition of the lock pin44 in cooperation with the operation of the loading arm swing mechanism7. Thus, the support frame 4 is floatingly supported through the dampers5 to the frame 3. Thus, the playback preparatory operation is completed.Then, the spindle motor 30 is driven to rotate the disk 101 or 106together with the turntable 29. When the disk 101 or 106 is rotated, alaser beam is irradiated from the readout head (not shown). The readouthead is moved in the radial direction of the disk 101 or 106 to therebyreproduce the music recorded in the disk 101 or 106.

As described above, according to the present invention, even if thesmall diameter disk is inserted into the disk insertion opening whilebeing displaced from the center thereof, it is possible to accuratelyposition the disk on the clamp position of the turntable. Also, thecentering arms of the centering mechanism are provided on the lowersurface of the clamper arm, whereby the centering operation for the diskis performed in the vicinity of the clamp position of the disk tothereby more exactly center the disk. Furthermore, the centeringmechanism is not provided in the vicinity of the disk insertion openingbut in the clamper arm. Therefore, it is unnecessary to insert the diskwhile widely opening the centering mechanism. This leads to a goodoperational feeling in the disk insertion step.

Accordingly, even if the small or large diameter disk is delivered, itis possible to more exactly perform the centering operation and toposition the disk exactly in the clamp position on the turntable.

What is claimed is:
 1. A disk playback apparatus comprising:a supportframe; a clamper arm swingably mounted on a rear portion of said supportframe; and a centering mechanism for guiding a large diameter disk and asmall diameter disk from a front side of said playback apparatus to aplaying position between said support frame and said clamper arm whenthe disk is inserted into the playback apparatus; said centeringmechanism comprising: a pair of centering arms rotatably mounted on saidclamper arm on a side of said clamper arm facing said support frame,said centering arms having centering pins extending therefrom forcontacting a circumferential edge of said disks in said playingposition; a centering lever slidably attached to said clamper arm andoperatively connected to said centering arms so as to cause said pair ofcentering arms to open and close in concert with each other; and a lockarm rotatably mounted about each of said centering pins for locking saidcentering arms, said lock arms each having an opening into which anengagement piece mounted at tip end portion of said centering armextends to form a stop mechanism against the rotation of said lock arm,said lock arm further including a lock pin projected upwardly andreleasably engaging with a lock recess portion of said clamper arm forlocking the swing motion of said centering arm, a lock release pin forrotating the lock arm to release the lock condition, and a lockarm-biasing spring interposed between said centering arm and said lockarm for biasing said lock pin in a direction in which said lock pin isengaged with said lock recess portion said lock arms allowing said pairof centering arms to be swingable only when both of said lock arms arereleased.
 2. The apparatus according to claim 1, wherein said centeringlever is made of a planer member and is provided above an upper surfaceof said clamper arm to be slidingly movable back and forth, saidcentering lever being connected to said pair of centering arms in asymmetrical relation.
 3. The apparatus according to claim 1, whereinsaid pair of centering arms are symmetrically provided, each centeringarm including a centering pin implanted in a forward end portion of theassociated centering arm, said centering pins being brought into contactwith the circumferential edge of the disk and extending toward saidsupport frame, wherein a distance between two centering pins are set sothat, when the small diameter disk is clamped by said clamper arm, saidcentering pins are out of contact with said small diameter disk.
 4. Theapparatus according to claim 1, further comprising a guide meansprovided near a disk insertion opening for guiding the large diskhorizontally and the small disk upward to the clamper arm.
 5. Theapparatus according to claim 1, wherein said centering mechanism furtherincludes a disk guide plate for guiding the disk to the clamp position,said guide plate being mounted on a lower surface of said clamper arm,said guide plate having a disk guide recess having an opening facing adirection of disk insertion.
 6. The apparatus according to claim 1,wherein said centering mechanism further includes an escape arm providedswingably on said clamper arm and engaged with said centering lever,wherein said escape arm holds said pair of centering arms in the opendirection through said centering lever when the disk is rotated andmaintains a non-contact condition between the disk and a contact portionof each of said centering arm.
 7. The apparatus according to claim 6,wherein said escape arm is urged to push rearwardly said centering leverand to bias the pair of centering arms inwardly by an escape arm springinterposed between said clamper arm and said escape arm, and an outwardend portion of said escape arm is engaged with a converting armswingably mounted on said support frame for being retained at differentpositions.
 8. The apparatus according to claim 7, wherein a firstprojection and a second projection for retaining said outward endportion of said escape arm are provided in an upper portion of saidconverting arm, and an engagement pin is provided for limiting a swingmotion range of said clamper arm by engaging with a guide groove of saidclamper arm.